1. Related Applications
The present application is related to patent applications 08/104,687, titled START RATIO ENGAGEMENT CONTROL SYSTEM AND METHOD; 08/104,699, titled SCROLLING GEAR RATIO SELECTION CONTROL SYSTEM AND METHOD; and 07/935,937, titled START GEAR RATIO CONTROL SYSTEM AND METHOD, all assigned to the assignee of this application, Eaton Corporation, and all effectively filed the same day as this application, Aug. 27, 1992.
2. Field of the Invention
The present invention relates to a control system and method for a semi-automatic mechanical transmission system, including a manually operated shift selector, for automatically controlling the changing or shifting of transmission gear ratios on a vehicle, while leaving the vehicle driver or operator some residual measure of control. In particular, the present invention relates to a control system and method for the semi-automatic control of a mechanical change gear transmission including means for automatically executing automatically determined and displayed allowable driver selected transmission ratio shifts, including automatic control of the vehicle master clutch. In one embodiment, a clutch pedal is provided and the master clutch operation is automated in all but start from stop situations. More particularly, the present invention relates to a system and method for controlling a semi-automatic mechanical transmission wherein a single downshift request made at a time when the vehicle is at rest, the master clutch is disengaged and the transmission is engaged in a relatively high (non start) ratio, is interpreted as a request for a direct shift into transmission neutral, or possibly into a preselected start from stop ratio, and/or a single upshift request made at a time when the vehicle is at rest, the master clutch is disengaged and the transmission is in transmission neutral, is interpreted as a request for a direct shift into a preselected start ratio.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks and/or coaches, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith are well known in the prior art. Such fully automatic change gear transmissions include transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio and automated mechanical transmissions utilizing electronic, hydraulic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065; 4,361,060; 5,050,079 and 5,109,729, the disclosures of which are hereby incorporated by reference.
Such fully automatic change gear transmissions can be unacceptably expensive, particularly for the largest heavy-duty vehicles which are not typically sold in high volumes. Additionally, those automatic change gear transmissions utilizing pressurized fluid and/or torque converters tend to be relatively inefficient in terms of power dissipated between the input and output shafts thereof. Moreover, many vehicle operators like to control the selection of the gear ratios, particularly since they can see and/or know the nature of the road ahead and/or of the load being carried.
The above drawbacks have been minimized by providing a semi-automatic mechanical transmission control wherein automatic changing between a plurality of gear ratios is provided while normally permitting the driver to choose when to make a particular gear ratio change and whether to select the immediately consecutive ratio up or down or to skip one or more ratios. Furthermore, the semi-automatic control system prohibits engagement of a driver selected higher ratio, i.e. an upshift, that would cause the engine speed to decrease below the idle speed, i.e. would cause stalling and/or over-stressing at low speeds of the engine, and of a lower ratio, i.e. a downshift, if such a change would cause over-speeding of the engine. It is noted that with manual mechanical transmissions such over-speeding of the engine can occur due to a improper downshift even though the engine speed may be governed against accelerating above the governed engine RPM. Examples of such a semi-automatic transmission control can be seen by reference to U.S. Pat. Nos. 4,648,290; 4,800,360; 4,930,081 and 4,930,078, the disclosures of which are incorporated herein by reference.
While the above-described semi-automatic mechanical transmission control does provide a very desirable semi-automatic control, the control was subject to improvement as, if the driver or operator desired a shift into neutral or into a selected transmission start ratio while the vehicle was at rest, the driver was required to identify the currently engaged ratio, to calculate the number of steps from the currently engaged ratio to neutral or the selected start ratio and to then move the selector lever that number of times in the upshift or downshift direction. This was particularly a concern in modern mechanical transmissions for heavy-duty vehicles which may have 9, 10, 12, 13, 16 or 18 forward speed ratios and wherein any one of the first seven ratios may be appropriate start ratios under certain conditions. Examples of such multi-speed mechanical transmissions may be seen by reference to U.S. Pat. Nos. 4,735,109 and 4,754,665, the disclosures of which are incorporated herein by reference.